This invention pertains to an impingement food preparation oven, and more particularly to an improved air delivery system for an impingement food preparation oven for providing uniform cooking temperatures for a food product.
Typically, an impingement food preparation oven comprises an enclosure having a cooking chamber with a food support member therein, and a plurality of heat ducts generally disposed above and below the support member for directing a flow of heated air against the food product. The flow of heated air is supplied to the air ducts through their respective openings by a plenum, and a fan device is disposed within an opening of the plenum for directing the flow of heated air therein. Heating elements are provided for heating the air before being drawn by the fan into the plenum.
Naturally, one of the objects of an oven is to provide a uniform cooking temperature for evenly cooking a food product therein, and this object is primarily a function of the flow of heated air within the oven enclosure. A problem too often occurring with some earlier ovens is their inability to provide proper air flow to evenly cook a food product, and generally several factors are the cause thereof.
One of these factors is the use of a paddle-type fan for drawing air from the enclosure into the plenum. These types of fans move the air in a rotating fashion with some axially directed movement, but with a greater portion of the movement being radially directed. Since the fan is mounted generally facing the front wall openings in the plenum, which are connected to the air ducts, the direction of flow of air is not satisfactorily axially directed from the fan to the ducts. Further, since the radial velocity component of the air flow tends to be greater than the axial velocity component, air buffeting is developed within the plenum caused by a succeeding fan paddle hitting or contacting the air volume moved by a preceding fan paddle. This buffeting of air also results in a less than desirable air flow through the plenum, and is also a source of undesirable noise during operation of the oven.
Another factor affecting the desired air flow is the front wall of the plenum, which is in some cases a flat surface facing towards the fan. The flat surface of the plenum front wall tends to retard the flow of air through the plenum, thereby creating an undesirable build up of static pressure therein. This static pressure does not allow for a smooth dynamic flow of air from the fan through the plenum and to the air ducts, but instead tends to rather push the air from the plenum into the air ducts. Moreover, this static pressure not only prevents smooth air flow, but also causes the plenum to be a soure of heat loss due to the pressure buildup therein.
In some earlier ovens, the plenum front wall is provided with a single tapering surface that tapers from the front wall opening inwardly of the plenum toward the fan. This type of plenum front wall is intended to evenly distribute a flow of air directed thereagainst into the air ducts. However, when used in conjunction with the above-described paddle-type fan, the tapering surface is not completely effective in dividing a swirling or rotating air flow into the air ducts.
Thus, the above plenum and fan assemblies in the earlier ovens generally do not provide an equal distribution of heated air to the ducts, thereby resulting in unsatisfactory heat distribution through the air ducts and an unevenly cooked food product. Further, since the heat of the flow of air from the air ducts is not evenly or uniformly distributed, those ovens utilizing a conveyor assembly to convey a food product through the cooking chamber do not have the versatility of operating the conveyor in both a left-to-right and right-to-left directions for cooking.